As a result of recent active genome analyses and studies, a clarification of the human genome constituted of a sequence of about 3 billions of deoxyribo nucleic acids (DNA) has almost been accomplished. The trend is now shifting to discoveries and clarifications of genes which are sources of gene information and, further, to clarifications of single-nucleotide polymorphisms (SNPs) which affect the physical constitution of individuals. Various genes and gene information have been clarified by the studies, and synthesis of a compound which controls the gene information in a specific manner is considered to be a useful process of a drug discovery technology of new era.
The present inventors have focused and have been studying on distamycin, an antibiotic, which is known to selectively bond to a site of a DNA abundant with AT base pairs. As a part of the study, the inventors have synthesized systematic distamycin derivatives by combining a pyrrole amide which is a constituent unit of distamycin and an imidazole amide which is a derivative of the pyrrole amide and has been conducting biochemical researches on the thus-obtained compounds. As a result of the researches, the inventors have clarified that each of the compounds is capable of selectively bonding with a specific site of DNA and the selectivity is defined by an order of pyrrole amide (Py) and imidazole amide (Im).
Further, the inventors have found a systematic screening method for conducting a cytotoxicity test on the known cancer cells by using the synthesized pyrrole-imidazole polyamides. This method is a simultaneous and easy screening method of the compounds targeting on DNA sequence specific to a certain cancer cell, which DNA sequence is being clarified in the human genome project. In the case where the number of pyrrole-imidazole amides, which are the constituent units, is 8, there are 256 combinations. By screening those compounds simultaneously, it is possible to systematically select cytotoxic compounds. The system is innovative since it enables to derive a useful substance which uniquely suits a target gene from the DNA selective compounds (pyrrole-imidazole polyamides) of a countless combinations. The present inventors have already filed a patent application of the invention (JP-A-2001-136974).
The synthesis of pyrrole-imidazole polyamide has been conducted through the liquid phase method, but this method is not appropriate for the synthesis of a different type.
On the other hand, as a solid phase synthesis of a pyrrole-imidazole polyamide, the t-BOC method has been developed by Dr. Dervan of California Institute of Technology, U.S.A. (J. Am. Chem. Soc., 1996, 118, 6141–6146); however, due to its strict reaction conditions, the method has a difficulty in synthesizing a long chain pyrrole-imidazole polyamide and is poor in applicability. Further, since the method does not use commercially available protein (peptide) synthesizers, it also has a difficulty in transferring a protein. Moreover, since the method has a difficulty in synthesizing a polyamide having a carboxyl group at its end and is poor in efficiency in excising the end from the solid phase as a carboxylic acid residue, it is difficult to impart a new reactivity to the obtained long chain pyrrole-imidazole polyamide by direct modification.
Further, though Fmoc synthesis method of polypyrrole has been reported by Dr. Mascarenas of Spain and Dr. Bruice of California University of U.S.A. (Tetrahedron Lett., 1999, 40, 3621–3624; J. Am. Chem. Soc., 2001, 123, 2469–2477), the polypyrrole cannot exactly distinguish DNA sequences because the imidazole amide is not transferred thereinto.